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TPS92690: PWM frequency dimming range

Rohit J
Intellectual 850 points
Part Number: TPS92690
Other Parts Discussed in Thread: TPS92691

Hi,


I was looking at TPS92690 for my LED driving needs. I wasn't able to find any recommended PWM frequency range in the datasheet. Can you provide a recommended range?

Thanks,

Rohit Joshi

  • 0
    TI__Mastermind 25500 points

    Hello Rohit,

    There isn't really a limit but it really depends on what kind of dimming range you need. This part PWM dims basically with a simple turn-on/turn-off type of operation. It does keep COMP charged for faster operation but the rising and falling LED current edges are not extremely fast.

    So there is no lower limit really, but you would likely want to use 100Hz or above to avoid seeing flicker. The maximum practical for any sort of range is probably around 1kHz or so. It all depends on operating points and external components. For an example of what I mean you can look at the boost EVM user's guide. You will notice that under those conditions and with that BOM the minimum ON time during PWM dimming where you actually reach the regulation current point is around 250us (see the 5% PWM dimming scope shot).

    Basically the lower the frequency the more range and linearity you get. If the TPS92690 is not fast enough for what you need you could consider the TPS92691. They are similar devices but the 691 includes an LED string disconnect FET driver so that the current rise/fall times are much faster.

    Regards,

    Clint